The authors of this study note there is some observational evidence to suggest that selenium may have a role in asthma, including a UK epidemiological study which found that the dietary intake of selenium in asthmatics was lower than controls. Despite this, only one randomised controlled trial has prospectively assessed the effect of selenium supplementation on adult asthmatics; this reported improvement based on a composite clinical evaluation, but no improvement in individual objective measures such as lung function and bronchial hyper-responsiveness. This study had several limitations, including the study size (n=24) and its short duration (14 weeks). The authors therefore carried out a larger randomised double-blind, placebo-controlled trial of selenium supplementation, of longer duration, in adults with asthma living in London, to see whether supplementation led to improvements in asthma-related quality of life and other measures of asthma severity. Potential participants were identified from 1) adult asthmatics that had taken part in one of two population-based studies conducted in Greenwich or Lambeth, Southwark and Lewisham (LSL); 2) advertisements in local papers and by email circulated at King’s College London, and 3) patients aged 18-54 who had received a prescription for inhaled corticosteroids in the previous six months (12 GPs in LSL). Potential participants were screened to confirm that they had had asthma symptoms in the last month, and were not taking a supplement containing selenium. Exclusion criteria included pregnancy or lactation, history of renal or liver disease; yeast intolerance; inability to perform spirometry satisfactorily, and inability to swallow tablets. A total of 197 eligible patients were randomised to receive either a high-selenium yeast preparation (SelenoPreciseTM 100 mcg daily, n=99) or placebo (yeast only, n=98) for 24 weeks. There was an initial three week run-in period; those who suffered gastro-intestinal side effects or who took less than 80% of the tablets were excluded from the main trial. The primary outcome was asthma-related QoL score; secondary outcomes included Forced Expiratory Volume in one second (FEV1), FEV1/Forced Vital Capacity (FVC), mean morning PEF, PEF variability, mean morning and evening asthma symptom scores, waking at night with asthma, increased bronchodilator use, and mean bronchodilator usage. Over 75% of patients included in the trial were taking inhaled corticosteroids at baseline, with a mean age of 40 years and a mean BMI of 28. The average QOL score at baseline was 1.46 in the placebo group and 1.39 in the selenium group; average FEV1 results were 2.64 and 2.66 respectively (76.67% and 79.7% of that predicted). The main results were as follows: • There was a 48% increase in plasma selenium between baseline and end of trial in the active treatment group, but no change in the placebo group. • Whilst QoL score improved more in the active treatment group than in the placebo group, the difference in change in score between the two groups was not significant (-0.05 (95% CI: -0.19 to 0.09); P=0.47). • Selenium supplementation was not associated with any significant improvement in secondary outcomes compared with placebo. The authors note that the results were very similar when the analyses were repeated to take into account the potential confounders at baseline; there was also no significant treatment effect when the results were stratified according to smoking status, asthma severity, use of inhaled steroids at baseline, or plasma level of selenium. They conclude that they were unable to demonstrate any clinical benefit of selenium supplementation on adults with asthma.